When you think about engine exhaust polluting the air, you probably have automobiles in mind. But did you know your gas lawnmower deserves some of the blame, too?

Like their larger counterparts, small engines also spew greenhouse gases. A study published in Environmental Science and Technology in 2001 reported that, in just one hour of mowing, a gasoline lawnmower sends as many pollutants into the environment as a 100-mile road trip.

(Although to be fair, the numbers given for this stat vary from different sources. More recent figures from the EPA say that one hour of lawnmower use can be equated to just a 45-mile road trip.)

The EPA does have a dizzying array of regulations for small spark-ignition engines (although trying to figure out what they mean may literally make you dizzy). While new lawnmowers must pass these standards over the engine’s expected lifetime, these standards are not enforced beyond the manufacturer. Additionally, there is little to no effort to bring older models up to these standards.

That 2001 Environmental Science and Technology study recommended that lawnmowers and other small engines follow the path of automobiles and be equipped with catalytic converters to help keep air clean.

A group of students from the University of California, Riverside are hoping to do just that with the development of a simple add-on contraption that can remove 93 percent of pollutants from lawnmower exhaust.

And, they expect it would only cost about $30 for one of the devices, which could be easily retrofitted onto existing lawnmowers.

The device would easily and unobtrusively attach to existent lawnmowers. Credit: UCR

Their device—a catalytic converter for your mower—is a simple L-shaped stainless steel pipe. It contains a metal mesh filter to remove initial pollutants from the exhaust. The device then douses the exhaust stream with an ultra-fine mist of urea solution to prime the air for catalysis.

The urea-primed-but-still-polluted air then passes through a ceramic catalytic support, converting harmful nitrogen oxide and ammonia into neutral nitrogen gas and water. According to an email from the students’ adviser Kawai Tam, the team employed a commercially available cordierite for the ceramic substrate.

According to the UCR press release, “When they tested the device it reduced the following harmful pollutants: carbon monoxide by 87 percent; nitrogen oxides by 67 percent, and particulate matter by 44 percent. With the improved version of the device, 93 percent of particulate matter emissions were eliminated.”

The project began with a prior group of students, who passed the torch for further improvements and refinements. The current team—which calls themselves NOx-Out—improved the original device with the addition of the catalytic substrate, stainless steel mesh filter (replacing a quartz one), a muffler, and a new L-shaped design to the device.

The project will once again follow the academic lineage to the next incoming group of students, who will make further improvements that will hopefully get the device closer to commercial availability.